Of the 30,000 infants born annually with congenital heart disease, more than one-third will require cardiac surgery early in life. Recent dramatic reductions in surgical mortality have been accompanied by the recognition that survivors frequently suffer adverse neurologic sequelae, often attributable to the support techniques used to protect vital organs during cardiac repair. The two major support techniques used in repair of complex congenital heart disease in infancy are: 1) deep hypothermia with total circulatory arrest ("circulatory arrest") and 2) deep hypothermia with continuous low-flow cardio-pulmonary bypass ("low- flow bypass"). We propose to compare the incidence of brain injury after use of circulatory arrest versus low-flow bypass. Our goals will be pursued in a prospective, randomized, blinded, single- center trial using a homogenous population of infants with d- transposition of the great arteries requiring surgery within the first month of life. The two support techniques will be compared specifically with respect to three dimensions of brain injury: 1) Brain structure will be assessed preoperatively and at specific intervals postoperatively to detect both transient and long-term structural injury. Methods of evaluation will include cranial ultrasound and magnetic resonance imaging (MRI); (2) Brain function will be assessed preoperatively and at specific intervals postoperatively by neurologic examination and electroencephalography; 3) Cognitive and motor development will be evaluated one year after surgery using standardized psychometric testing. The outcomes of primary interest (i.e., MRI, neurologic examination, and psychometric testing) will be measured at the one- year evaluation, to maximize relevance to long-term prognosis. Secondary outcome variables will be measured in the immediate postoperative period. The structure of the study will also facilitate identification of perioperative risk factors for brain injury other than the randomized support techniques. The inferences reached in this study population should be broadly generalizable to children with other forms of congenital heart disease undergoing early repair and thus should have substantial impact on clinical practice. Furthermore, identification of other perioperative risk factors will provide insight into causes of diffuse and focal brain injury. These data are sorely needed to reduce the incidence (and hence, personal and financial costs) of neurologic sequelae following major cardiovasculary surgery.